A field of force associated with changing electric fields, as when electric charges are in motion. Magnetic fields exert deflective forces on moving electric charges. Most magnets have magnetic fields as a result of the spinning motion of the electrons orbiting the atoms of which they are composed; electromagnets create such fields from electric current moving through coils. Large objects, such as the earth, other planets, and stars, also produce magnetic fields. See Note at magnetism.

magnetic field definition

A magnetic field is said to exist in a region if a force can be exerted on a magnet. If a compass needle is deflected when it is put at a particular location, we say a magnetic field exists at that point, and the strength of the field is measured by the strength of the force of the compass needle. The Earth, the sun, and the Milky Way galaxy all have magnetic fields. All known magnetic fields are caused by the movement of electrical charges. Electrons in orbit in atoms give rise to magnetic fields, so that every atom is, like the Earth, surrounded by a magnetic field. (Seemagnetandmagnetism.)